1. Field of the Invention
The present invention relates to a method of printing a material web, particularly a paper web. The method includes applying a printing ink on the material web, drying the material web with the use of heat and subsequently cooling the material web.
The present invention also relates to an apparatus for printing a material web including a printing unit, a drying section and a cooling section.
2. Description of the Related Art
When printing a material web, the printing ink is in most cases applied in liquid form. Because of the high travel speeds of paper webs used today, the ink is usually not yet sufficiently dried when the paper web leaves the printing unit. In order to nevertheless be able to carry out further processing steps immediately after printing, for example, cutting, folding, stacking and stitching or stapling of the printed web, the web is guided through a dryer section in which the printing inks are dried with the use of heat. However, in the warm state the printing inks have a certain stickiness which is a disadvantage when printed sheets are stacked because the sheets then adhere to each other. For this reason, the material web is cooled after drying.
It has now been found that, while the cooled material web is no longer sticky, the material web has a number of other properties which make further processing of the material web more difficult or which lead later during use to unpleasant concomitant phenomena. For example, rattling or creasing of the paper reduces the comfort of the person looking at the paper. Accordingly, an elimination of these phenomena would be desirable. However, more critical are changes in the paper web which make the further processing of the paper web more difficult. For example, after such a treatment of the paper web, it can frequently be observed that the web becomes brittle which, when the web is folded, sometimes leads to breaks at the fold. Stapling also becomes more difficult because the staple penetrates unimpededly through one or more paper layers.